Vane-type fluid pump

ABSTRACT

A vane-type pump in which the vanes are hydrostatically balanced whereby they are urged outward only by centrifugal force. The cam ring sealing surfaces rise in the sealing zones to assure contact with the vanes.

United States Patent 1 1 Schmitz 1 1 Jan. 16, 1973 541 VANE-TYPE FLUIDPUMP 2,545,231; 3/1951 MacMillin ct al. ..418/268 2,612,115 9/1952 Ernst..418/238 176] lnvcntor. Albert A. Schmltz, "5217 Durand 1054.357 M962McGm 418/77 Avenue Pleamm 3,086,475 4/1963 R0580" 1 .4111/2611 22 Filed:Dec. 22 19 9 3,180,271 4/1965 Hartmann ..411'l/2()8 X 3,221,665 12/1965Hartmann "418/268 X [21] Appl. No.2 886,982 3,361,076 1/1968 Davis ..41x31 Related US. Application Data FOREIGN PATENTS OR APPLICATIONS [63]Continuation-impart of Ser. No. 739,359, June 24, 156,691 12/1952Austrafia ..418/268 1968, abandoned. 551,685 3/1943 Great Britain.....

433,488 8/1935 Great Britain ..418/257 [52] US. Cl ..4l8/31,418/268 511111.01 ..F01 21/16, F03C 3/00, F04C 15/04 Prvnary Exammer-wllllam Freeh[58] Field of Search ..418/31, 238, 267, 268, 27, Assistant ExammewlohnVrabhk 413 30 Attorney-Hume, Clement, Hume & Lee

[56] References Cited [571 ABSTRACT UNITED STATES PATENTS A vane-typepump in which the vanes are hydrostatically balanced whereby they areurged outward only 2,669,189 2/1954 DeLancey et a1. ..418/27 bycentrifugal force. The cam ring sealing surfaces rise 3,033,535 4/1963Krafft e1 in the sealing zones to assure contact with the vanes.3,187,676 6/1965 Hartmann ..418/31 1,965,388 7/1934 Ott ..418/31 12Claims, 3 Drawing Figures VANE-TYPE FLUID PUMP BACKGROUND OF THEINVENTION This application is a continuation-in-part of applicantsco-pending application, Ser. No. 739,359, filed June 24, 1968, and nowabandoned. The invention is in the field of fluid pumps. It relatesparticularly to reversible flow, vane-type fluid pumps.

Reversible flow, vane-type fluid pumps are, of course, generallywell-known. Such a pump is illustrated in the Wahlmark U. S. Pat. No.2,842,064, for example. In essence, a rotor, slidably mounting aplurality of radially disposed vanes in its periphery, rotates within aneccentrically arranged, annular chamber, and is effective to draw fluidinto the chamber through an inlet port and discharge it under pressurethrough an outlet port. By reversing the eccentricity of the chamber,the flow pattern is reversed.

In a vane-type fluid pump of this type, there is a normal tendency forfluid pressure in the chamber to urge the vanes into their slots, thusleaving a free path for fluid between the inlet and exhaust ports. Ifthe vanes were permitted to succumb to this urging, the pump would begrossly ineffective, of course. Accordingly, various means have beendevised to counter-act the pressure urging the vanes inwardly of theirmounting slots.

One means for obtaining this end is a fluid bleed system alternatelyconnecting the inlet and pressure zones of the chamber with the space ineach vane slot beneath a corresponding vane. This arrangement results ina pressure induced, radially directed, outward force being effective onthe vanes as they rotate. The result is considerable wear on the vanetips, which are urged with substantial force against the annular camring surface of the chamber.

Another means devised and employed in conventional vane-type fluid pumpsto assure operational engagement of the vanes with the cam ring surfaceis mechanical springs provided in the bases of the vane slots beneaththe vanes. The spring force needed to assure operational engagement ofthe vane tips under all operating conditions is, understandably,substantial. As a result, frictional wear of the vane tips and cam ringsurface is, once again, a detrimental factor.

SUMMARY OF THE INVENTION The present invention is embodied in a pumparrangement wherein the vanes are hydro-statically balanced in theirslots, thus neutralizing the radial fluid pressure forces normallyeffective on the vanes. Centrifugal force is sufficient to urge thevanes outwardly into engagement with the cam ring surface, and minimalfrictional wear results. The configuration of the vanes according to theinvention results in this hydro-static balance.

A subsidiary feature of the invention is embodied in the arrangement ofthe cam ring sealing surfaces relative to the axis of rotation of thepump rotor. As is wellknown, a force component tangential to the rotoris created as the vanes pass through the sealing zones between the inletzone and the pressure zone, tending to bind the vanes against the sidesof their respective slots. In the present invention, the sealingsurfaces are formed so their radii of curvature decrease in thedirection of vane rotation, except in oppositely extreme positions ofeccentricity relative to the rotor where a constant radius might beeffected, whereby as the vanes pass over these surfaces they are neverrequired to move in an outward direction in order to follow the surface.During this power phase of the pumping cycle, the vanes are then eitherstationary in their slots or are being moved slightly inwardly by a camsurface rise.

Thus, with the vanes hydrostatically balanced and the cam ring formed toeliminate outward movement of the vanes during their passage through thesealing zones, centrifugal force maintains the vane tips in contact withthe cam surface. Centrifugal force is sufficient to maintain excellentoperational engagement of the vane tips with the cam surface but isnever excessive so as to cause undue frictional wear on eithercomponent. Other features of the invention are found in a housingassembly including a unitary body in which bearing bores are easilymachined and heavy duty bearings maintained in perfect alignment. Theconstruction of the housing assembly is such that it is easily matchedto the width of the cam ring to control the clearance between the ringand thrust plates forming the sides of the housing assembly. The camring, in itself, has external dimensions sufficiently large to permitthe full side thrust of internal pressure to be balanced by an opposingfluid cushion.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view,partially in section, of a vane-type fluid pump embodying features ofthe present invention;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1; and

FIG. 3 is an enlarged sectional view through a portion of the pump rotorassembly at a cam ring sealing surface.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing,and particularly to FIGS. 1 and 2, a vane-type fluid pump embodyingfeatures of the present invention is illustrated generally at 4. Thepump 4 includes a housing assembly 5 which contains a drive assembly 6and a pumping cartridge 7.

The housing assembly 5 comprises a body 10 having an upper wall 11 and alower wall 12 formed unitarily with an annular front wall 15 and a rearwall 16. An annular bore 17 is machined in the front wall 15 and acorresponding bore 18 is machined in the rear wall 16. Removable sidewalls 20 and 21 are secured to the body member 10 by a plurality ofconventional machine screws 22. A fluid inlet-outlet port 25 is formedin the side wall 20 while another fluid inlet-outlet port 26 is formedin the side wall 21.

The pumping cartridge 7 is mounted within the housing assembly 5 on thedrive shaft 30 of the drive assembly 6. The shaft 30 is rotatably drivenby a prime mover such as a motor (not shown). The shaft 30 is rotatablymounted in the housing assembly 5 on substantially identical rotorbearing assemblies 31 and 32 at the front and rear of the body 10.

Each bearing assembly 31 and 32 comprises an inner race 35 journaled ona mating section of the drive shaft 30 and an outer race 38 seated in acorresponding annular bore 17 and 18 extending through the front wall l5and rear wall 16, respectively of the body member 10. A plurality ofconventional tapered roller bearings 43 are disposed between the bearingraces 35, and 38, in suitable carrier cages 44.

The outer bearing race 38 in the rear wall 16 of the body is seatedagainst an inwardly extending shoulder 50 in the bore 18. The innerbearing race 35 in the rear wall is seated, at its outermost end,against an annular shoulder 51 on the shaft 30. An end plate 53 mountinga resilient seal 54 encircles and forms an oil seal with the shaft 30 ina conventional manner. The

end plate 53 is secured to the rear wall- 16 of the body The innerbearing race 35 in the front wall 15 of the body 10 is retained on theshaft 30 by a lock-nut 60 in a conventional manner. The outer race 38 inthe front wall 15 is, in turn, retained in the bore 17 by an end plate61 secured to the body 10 by conventional machine screws 62. An O-ring63 acts as an oil seal.

The pumping cartridge 7 is disposed between and bracketed by the innerbearing races 35. The cartridge 7 includes a rotor assembly 70 mountedon the shaft 30 for rotation therewith. The rotor assembly 70 includes arotor disc 71 keyed to the central section of the shaft 30 in aconventional manner by a key 72. Radially disposed in the annularperiphery of the rotor disc 71 are a plurality of evenly spaced, vanereceiving slots 76. Vanes 80 embodying features of the present inventionare slidably received in corresponding slots 76.

The pumping cartridge 7 further includes a casing or cam ring 83encircling the rotor disc 71 and the radially extending vanes 80. Thecasing 83 defines a generally circular bore 84 in which the rotorassembly 71 is mounted for rotation. The bore 84 has a diametersubstantially larger than the diameter of the rotor disc 71. A chamber85 is thus defined between the bore 84 surface and the outer peripheryof the disc 71.

Enclosing this chamber 85 and retaining the vanes 80 in the slots 76,which extend transversely through the width of the rotor disc 71, arebracketing retainer plates 88. The retainer plates 88, which form thesides of the pumping cartridge 7 and are retained in this relationshipby abutment with the inner bearing races 35, hereinbefore discussed,maintain the casing 83 in axial alignment with the rotor disc 71, i.e.axially of the shaft 30. The lock-nut 60 ties the inner bearing races35, the retainer plates 88, the rotor assembly 70, and the shaft 30together.

Formed in the casing 83 on opposite sides thereof, in registry with theinlet-outlet ports 25 and 26 through side walls and 21, respectively,and the bore chamber 85, are inlet-outlet chambers 91 and 92. The upperand lower extremities 93, 95, 99 and 101, of these chambers 91 and 92define the angular limits of inlet discharge zones 107 and 108 in theannular chamber 85. intermediate the inlet discharge zones 107 and 108are the sealing zones 110 and 111 defined by surface sections 113 and114, respectively, in the bore 84. For reasons hereinafter discussed,the radii of curvature of the surface sections 113 and 114 decreaseslightly in the direction of rotation of the rotor assembly 70,relatively to the axis of the shaft 30, in all positions of the rotorassembly '70. [t is within the contemplation of the invention, however,that in positions of maximum eccentricity of the rotor assembly 70,portions of the surface sections 1 l3 and 1 14 might not decrease inradius relative to the shaft 30 but actually remain constant relativethereto, rather than increasing at any point.

As will readily be understood, the position of the easing 83 relative tothe axis of the shaft 30 and, accordingly, the axis of rotation of therotor assembly 70, determines both the direction of fluid flow and flowvolume of the pump 4 in operation. The casing 83 is thus verticallyslidable between the side walls 20 and 21 of the housing assembly 5 onbearing faces 120.

Each bearing face 120 is, according to the invention, formed with ashallow recess 121 therein. According to the invention, the surface areaof each recess 12] approximates in size the projected area of theinternal area of the casing 83 which is subjected to fluid pressure.During operation of the pump 4, these recesses 121 fill with fluid underpressure equal to the fluid pressure in the casing 83 interior, thusbalancing any forces tending to create excessive friction between thecasing 83 and the side walls 20 and 21.

To control flow direction and volume of the pump 4, the casing 83 ismoved vertically in the housing 5 through the medium of a control rod125. The control rod 125 extends through a suitably formed bore in thetop of the body 10 and carries a sealing O-ring 126. An annular flange127 on the lower end of the rod 125 slides loosely (from the side) intoa corresponding slot in the casing 83 to connect the rod to the casingfor vertical movement together.

According to the invention, the pumping cartridge 7 is positionedsecurely between the rotor bearings 31 and 32 so that the casing 83 neednot be restrained axially by the housing assembly 5 but is allowed tofloat and seek its own position relative thereto. As a result, axialforces imparted to the shaft 30 by outside means are not transmitted asthrust loading on the casing 83.

Turning now to the construction and arrangement of the vanes 80 in theirslots 76, it has been pointed out that they are subjected to balancedforces tending to urge them radially outward and inward of their slots,thus placing reliance on centrifugal forces alone to keep the vanes incontact with the casing or cam ring surface 84. To this end, the tip ofeach vane 80 is formed with a projection 130 extending in front of theleading face 131 of the vane. This projection is defined by a planarupper surface 132 inclined at an angle of approximately 45 to theleading face 131, and a planar lower surface 133 forming approximately a70 angle with the surface 132.

The lower surface 133, in turn, intersects an opposite lower planarsurface 137 of the vane tip to form a line" of contact with the cam ringsurface 84 in the exact plane of the vane face 131. Alternatively, thesurfaces 133 and 137 might be a continuous curved surface so disposedthat line contact with the casing 58 is effected in alignment with theplane of the face 131.

The opposite face 140 of the vane 80 is formed with fluid passagegrooves 141 extending between the lower planar surface 137 and the innerend surface 142 of the vane. Fluid pressure at the vane face 140 iseffective, through the grooves 141, on the inner end surface 142 of eachvane, as well as on the surface 137 of the vane. Since these surfacesare substantially equal in area, a

balanced radial thrust condition is effected. Similarly, fluid pressureat the face 131 of the vane is effective on both the upper surface 132and the lower surface 133 of the projection 130, which surfaces aresubstantially equal in area, to also create a balanced radial thrustcondition. A substantially fluid tight seal is formed between the face131 and the adjacent wall of the slot 76.

Referring again to FIG. 1, in operation of the pump 4 the rotor 71 isdriven in a counterclockwise direction by the shaft 30. With theeccentric arrangement of the casing 83 relative to the rotor 71 asillustrated in FIG. 1, the fluid flows in a direction from left toright, from the inlet-outlet port 25 to the inlet-outlet port 26.

The rotation of the rotor 71 produces centrifugal force which urges therotor vanes 80 outwardly against the cam ring surface 84 of the casing83. As each vane passes from the suction zone 107 into the sealing zone111, increased pressure is exerted against the face 131 of the vane,tending to bind the vane in its slot and overcome the centrifugal forceurging the vane outwardly. According to the invention, however, theradius of curvature of the sealing zone surface 114 in the casing 83decreases relative to the axis of the rotation of the rotor 71, in thedirection of rotation, thus effectively causing this surface 114 torise. During passage through this sealing zone 1 11, the vanes 80 arethus forced progressively inwardly by the surface 114, assuring contactof the vane tips with the surface and preventing fluid leakage past thevanes.

In traversing the discharge zone 108 of the chamber 85, the vanes 80 areagain free to respond to centrifugal force and follow the chamber wall84 to the sealing zone 110. Here the flow pressure in the discharge zone108 is cut off from the face 131 of each vane and unbalanced pressureagainst the face 140 again tends to bind the vane 80 in its slot 76.Once again, however, the rise in the sealing zone surface 113 maintainscontact with the vane tips and preserves the seal.

Control of the pump 4 volumetric output is effected by manipulation ofthe control rod 125. As the casing 83 is retracted toward a positionmore nearly concentric with the rotor 71, flow diminishes and finallyceases at the point of concentricity. Movement of the casing past thispoint of concentricity causes the flow to begin in the oppositedirection through the pump 4 and increase until the casing 83 hasreached the point of maximum eccentricity in the opposite direction tothat shown in FIG. 1.

A variable volume, reversible flow, vane-type pump has now beendescribed which produces a highly efficient pumping operation withminimum wear of moving components. The pump assembly has a compact bodyconstruction which is easily machined and fabricated to requiretolerances. Throughout the pump, fluid pressures reacting upon varioussurfaces are substantially balanced so as to minimize sliding frictionbetween components.

The pump has been described in terms of counterclockwise rotation sothat the faces 13] of the vanes 80 are leading" and the faces 140 aretrailing". This is the preferred mode of operation. However, it has beenfound that excellent performance is also obtained with the vanes 80reversed in their slots so that the slotted faces 140 become theleading" faces, and it is intended that this application cover such modeof operation.

While the embodiment described herein is at present considered to bepreferred, it is understood that various modifications and improvementsmay be made therein.

What is desired to be claimed and secured by Letters Patent of theUnited States is:

1. In a variable volume pump including a rotor formed with a pluralityof circumferentially spaced slots slidably receiving substantiallyradially extending vanes, radial movement of said vanes being controlledby a curved surface defining a chamber in a casing encircling saidrotor, said chamber having inlet and outlet means which define suction,discharge and sealing zones in said casing; the improvement wherein saidcurved surface defining said chamber in the region of said sealing zonesis formed in such a manner as to present to the rotor and vanes aconstant or decreasing radius in the direction of rotation of said rotorin all positions of said casing relative to the axis of rotation of saidrotor.

2. The improvement of pump of claim 1 further characterized by andincluding means for radially balancing said vanes in corresponding slotsso that centrifugal force is substantially the only force urging thevanes outwardly through the operational cycle of said pump.

3. In a variable volume pump including a rotor formed with a pluralityof circumferentially spaced slots slidably receiving substantiallyradially extending vanes, radial movement of said vanes being controlledby a curved surface defining a chamber in a casing encircling saidrotor, said casing formed with inlet and outlet means which definesuction, discharge and sealing zones in said chamber; the improvementwherein said curved surface defining said chamber in the region of saidsealing zone is formed in such a manner as to present to the rotor andvanes a decreasing radius in the direction of rotation of said rotor inall positions of said casing relative to the axis of rotation of saidrotor.

4. A variable volume-reversible flow pump comprising a housing withremovable side walls, a shaft in said housing rotatably supporting arotor formed with a plurality of circumferentially spaced slots slidablyreceiving substantially radially extending vanes, radial movement ofsaid vanes being controlled by a curved surface defining a chamber in acasing encircling said rotor, said casing formed with inlet and outletmeans which define suction, discharge and sealing zones in said chamber,said casing being slidably mounted between said side walls for movementrelative thereto and free to assume a position in axial alignment withsaid rotor, said casing being positionable for selection of the degreeand direction of eccentricity between said rotor and said chamber ofsaid casing, said eccentricity determining the volumetric displacementof said pump and the direction of the fluid flow, said curved surfacebeing formed with a decreasing radius in the region of said sealingzones in relation to the normal direction of rotation of said rotor.

5. In a variable volume pump including a rotor formed with a pluralityof circumferentially spaced slots slidably receiving substantiallyradially extending vanes, radial movement of said vanes being controlledby a curved surface defining a chamber in a casing encircling saidrotor, said casing formed with inlet and outlet ports defining suction,discharge and sealing zones in cooperation with said chamber surface andsaid rotor; the improvement wherein said curved surface defining theinner chamber of said casing in the region of said sealing zones isformed in such a manner as to present to the rotor and vanes a constantor decreasing radius in the direction of rotation of said rotor in allpositions of said casing relative to the axis of rotation of said rotor.

6. in a pump including a rotor formed with a plurality ofcircumferentially spaced slots slidably receiving substantially radiallyextending vanes, each of said vanes having a leading face and a trailingface, radial movement of said vanes being controlled by a curved surfacedefining a chamber in a casing encircling said rotor; the improvementwherein said casing is formed with inlet and outlet means which definesuction, discharge and sealing zones in said chamber, said curvedsurface defining said chamber in the region of said sealing zones beingformed in such a manner as to present to the rotor and vanes a constantor decreasing radius in the direction of rotation of said rotor in allpositions of said casing relative to the axis of rotation of said rotor,each of the vanes being formed so that its outer tip engages said curvedsurface only in single line contact and said single line contact issubstantially in the plane of one of said faces, radially extendingfluid passage means formed in said vane placing inner and outer endsurfaces of said vane in fluid communication through said passage means,one face of each of said vanes and the adjacent wall of eachcorresponding slot cooperating to form a substantially fluid tight sealbetween the vane and slot.

7. In a variable volume pump including a housing, drive shaft meansrotatably mounted in the housing, a rotor mounted on the drive shaftmeans and positioned between retainer plates, the rotor having aplurality of slots on its peripheral surface, and a substantiallyradially extending vane confined in each of said slots by a casinghaving an annular inner surface encircling said rotor to form a pumpingchamber therebetween, the improvement wherein said housing includes aunitary body having integral upper, lower, front and rear walls,removable side walls secured to said body to form a substantially closedhousing, said casing being slidably movable between said side walls,said retainer plates maintaining said casing in axial alignment withsaid rotor.

8. The improvement in a variable volume pump of claim 7 furthercharacterized by and including means for radially balancing said vanesin corresponding slots so that centrifugal force is substantially theonly force urging said vanes outwardly through the operational cycle ofsaid pump.

9. The improvement in a variable volume pump of claim 7 furthercharacterized in that said drive shaft means are rotatably supported bybearings mounted in said integral front and rear walls of said body.

10. The improvement in a variable volume pump of claim 7 furthercharacterized in that said casing is formed with inlet and outlet meanswhich define sue tion, discharge and sealing zones in said chamber, saidannular inner surface encircling said rotor in the region of saidsealinghzones bein formed in such a manner as to present to e rotor anvanes a constant or decreasing radius in the direction of rotation ofsaid rotor in all positions of said casing relative to the axis of saidrotor.

11. The improvement in a variable volume pump of claim 7 furthercharacterized by and including bearing faces on said casing slidable onsaid side walls, and recess means formed in each of said bearing faces,said recess means being in fluid communication with said pumpingchamber.

12. The improvement in a variable volume pump of claim 11, furthercharacterized in that the surface area of each recess means approximatesin size the corresponding projected area of the interior of the casingwhich is exposed to fluid pressure so as to balance fluid pressureforces between said casing and said side walls.

1. In a variable volume pump including a rotor formed with a pluralityof circumferentially spaced slots slidably receiving substantiallyradially extending vanes, radial movement of said vanes being controlledby a curved surface defining a chamber in a casing encircling saidrotor, said chamber having inlet and outlet means which define suction,discharge and sealing zones in said casing; the improvement wherein saidcurved surface defining said chamber in the region of said sealing zonesis formed in such a manner as to present to the rotor and vanes aconstant or decreasing radius in the direction of rotation of said rotorin all positions of said casing relative to the axis of rotation of saidrotor.
 2. The improvement of pump of claim 1 further characterized byand including means for radially balancing said vanes in correspondingslots so that centrifugal force is substantially the only force urgingthe vanes outwardly through the operational cycle of said pump.
 3. In avariable volume pump including a rotor formed with a plurality ofcircumferentially spaced slots slidably receiving substantially radiallyextending vanes, radial movement of said vanes being controlled by acurved surface defining a chamber in a casing encircling said rotor,said casing formed with inlet and outlet means which define suction,discharge and sealing zones in said chamber; the improvement whereinsaid curved surface defining said chamber in the region of said sealingzone is formed in such a manner as to present to the rotor and vanes adecreasing radius in the direction of rotation of said rotor in allpositions of said casing relative to the axis of rotation of said rotor.4. A variable volume-reversible flow pump comprising a housing withremovable side walls, a shaft in said housing rotatably supporting arotor formed With a plurality of circumferentially spaced slots slidablyreceiving substantially radially extending vanes, radial movement ofsaid vanes being controlled by a curved surface defining a chamber in acasing encircling said rotor, said casing formed with inlet and outletmeans which define suction, discharge and sealing zones in said chamber,said casing being slidably mounted between said side walls for movementrelative thereto and free to assume a position in axial alignment withsaid rotor, said casing being positionable for selection of the degreeand direction of eccentricity between said rotor and said chamber ofsaid casing, said eccentricity determining the volumetric displacementof said pump and the direction of the fluid flow, said curved surfacebeing formed with a decreasing radius in the region of said sealingzones in relation to the normal direction of rotation of said rotor. 5.In a variable volume pump including a rotor formed with a plurality ofcircumferentially spaced slots slidably receiving substantially radiallyextending vanes, radial movement of said vanes being controlled by acurved surface defining a chamber in a casing encircling said rotor,said casing formed with inlet and outlet ports defining suction,discharge and sealing zones in cooperation with said chamber surface andsaid rotor; the improvement wherein said curved surface defining theinner chamber of said casing in the region of said sealing zones isformed in such a manner as to present to the rotor and vanes a constantor decreasing radius in the direction of rotation of said rotor in allpositions of said casing relative to the axis of rotation of said rotor.6. In a pump including a rotor formed with a plurality ofcircumferentially spaced slots slidably receiving substantially radiallyextending vanes, each of said vanes having a leading face and a trailingface, radial movement of said vanes being controlled by a curved surfacedefining a chamber in a casing encircling said rotor; the improvementwherein said casing is formed with inlet and outlet means which definesuction, discharge and sealing zones in said chamber, said curvedsurface defining said chamber in the region of said sealing zones beingformed in such a manner as to present to the rotor and vanes a constantor decreasing radius in the direction of rotation of said rotor in allpositions of said casing relative to the axis of rotation of said rotor,each of the vanes being formed so that its outer tip engages said curvedsurface only in single line contact and said single line contact issubstantially in the plane of one of said faces, radially extendingfluid passage means formed in said vane placing inner and outer endsurfaces of said vane in fluid communication through said passage means,one face of each of said vanes and the adjacent wall of eachcorresponding slot cooperating to form a substantially fluid tight sealbetween the vane and slot.
 7. In a variable volume pump including ahousing, drive shaft means rotatably mounted in the housing, a rotormounted on the drive shaft means and positioned between retainer plates,the rotor having a plurality of slots on its peripheral surface, and asubstantially radially extending vane confined in each of said slots bya casing having an annular inner surface encircling said rotor to form apumping chamber therebetween, the improvement wherein said housingincludes a unitary body having integral upper, lower, front and rearwalls, removable side walls secured to said body to form a substantiallyclosed housing, said casing being slidably movable between said sidewalls, said retainer plates maintaining said casing in axial alignmentwith said rotor.
 8. The improvement in a variable volume pump of claim 7further characterized by and including means for radially balancing saidvanes in corresponding slots so that centrifugal force is substantiallythe only force urging said vanes outwardly through the operational cycleof said pump.
 9. The impRovement in a variable volume pump of claim 7further characterized in that said drive shaft means are rotatablysupported by bearings mounted in said integral front and rear walls ofsaid body.
 10. The improvement in a variable volume pump of claim 7further characterized in that said casing is formed with inlet andoutlet means which define suction, discharge and sealing zones in saidchamber, said annular inner surface encircling said rotor in the regionof said sealing zones being formed in such a manner as to present to therotor and vanes a constant or decreasing radius in the direction ofrotation of said rotor in all positions of said casing relative to theaxis of said rotor.
 11. The improvement in a variable volume pump ofclaim 7 further characterized by and including bearing faces on saidcasing slidable on said side walls, and recess means formed in each ofsaid bearing faces, said recess means being in fluid communication withsaid pumping chamber.
 12. The improvement in a variable volume pump ofclaim 11, further characterized in that the surface area of each recessmeans approximates in size the corresponding projected area of theinterior of the casing which is exposed to fluid pressure so as tobalance fluid pressure forces between said casing and said side walls.